In various environments, for example, in soil, microorganisms play an important role in converting and cycling substances. For example, in order for nitrogenous fertilizer to be converted in agricultural land so as to be taken in by agricultural crops, microorganisms need to perform “nitrification”.
Owing to the progress of the chemosynthesis technology, farming methods using chemical fertilizer have been widely performed in the postwar period. However, due to an increased demand for consumers' safety and safe agricultural products, or for the sake of sustainable agricultural production, shift to organic farming or natural farming is increasingly taking place in various regions. In these farming methods, practical use of ecosystems in soil is important. In addition, agricultural products use and absorb components in soil to grow, and thus appropriate evaluation, control, and improvement of soil are considered to contribute to improvement in profitability and productivity.
However, hitherto known soil evaluation has mainly involved analysis for chemical farming, and thus the evaluation has mainly been based on physicochemical properties such as concentration of inorganic ions and pH, whereas activity of microorganisms has not been taken into consideration (see non-patent literatures 1 and 2).
Thus, it has been impossible to clearly determine whether soil is suitable for cultivation of agricultural crops using organic farming or natural farming, or whether soil requires improvement.